Method for making fin-free mutli-bored rubber sheets

ABSTRACT

A method for making fin-free multi-bored rubber sheets by pressing a starting raw-rubber sheet against a die having a plurality of die projections. A carrier sheet, which can integrally adhere to those portions of the starting rubber sheet which are strongly pressed thereto by the free ends of the die projections, is overlaid on the starting raw-rubber sheet prior to the pressing. Thereby, upon completion of the pressing operation, the carrier sheet is separated from the starting rubber sheet, for ensuring the complete elimination of the fins at the bored portions of the rubber sheet.

United States Patent Ogata 51 3,699,204 [451 Oct. 17, 1972 [54] METHODFOR MAKING FIN-FREE MUTLI-BORED RUBBER SHEETS [72] Inventor:

[73] Assignee: Bridgestone Tire Company Limited,

Tokyo, Japan [22] Filed: May 18, 1971 [211 Appl.No.: 144,443

Nobuo Ogata, Kamakura, Japan [30] Foreign Application Priority Data7/1955 Marsch ..264/316 2,712,159 2,962,764 12/1960 Trojanowski et al..264/316 X 3,557,276 1/1971 Williams ..264/316 Primary Examiner-RobertF. White Assistant Examiner-Allen M. Sokal AttorneyStevens, Davis,Miller & Mosher [57] ABSTRACT A method for making fin-free multi-boredrubber sheets by pressing a'starting raw-rubber sheet against a diehaving a plurality of die projections. A carrier sheet, which canintegrally adhere to those portions of the starting rubber sheet whichare strongly pressed thereto by the free ends of the die projections, isover- .laid on the starting raw-rubber sheet prior to the pressing.Thereby, upon completion of the pressing operation, the carrier sheet isseparated from the starting rubber sheet, for ensuring the completeelimination of the fins at the bored portions of the rubber sheet.

4 Claims, 12 Drawing Figures PATENTEDum 11 m2 SHEET 3 0F 3 Fig. 1/

INVENTOR ATTORNEY METHOD FOR MAKING FIN-FREE MUTLI-BORED RUBBER SHEETSThis invention relates to a method for making finfree multi-bored rubbersheets, and more particularly to a simple and inexpensive method formaking multibored rubber sheets whose bores are cleanly formed in afin-free manner with accurate diametrical and positional dimensions.

The use of multi-bored rubber sheets has recently been expanded, forinstance, as vibrating sifting screens, because such multi-bored rubbersheets do not produce any annoying noise.

The dimensions of holes in such multi-bored rubber sheets, inclusive ofthe hole diameters as well as spacing therebetween, must be accurate,from the standpoint of service life, especially in the case of vibratingsifting screens.

According to a conventional process for making such multi-bored rubbersheets, a shaping press is used, which includes a surface plate forreceiving a die having a plurality of die projections f formed thereon-Apressure board having a flat surface cooperates with such shaping,press. A starting raw-rubber sheetis placed on the surface plate of theshaping press, and then the pressure board presses the startingraw-rubber sheet to produce the desired multi-bored rubber sheet shaving holes h bored therethrough. With such known process, the rubbersheet being shaped can be vulcanized immediately after the shaping,simply by heating the shaping press and the pressure board. In the spacebetween the pressure board and the free end surfaces of the dieprojections, the raw rubber material tends to flow toward the peripheryof the holes h of the sheet s. It is, however, inevitable that a part ofthe rawrubber material remains in the aforesaid space between thepressure board and the die projection, and such I residual raw-rubbermaterial becomes fins p: at the edges of holes h in the finished sheets. i

' In order to remove such fins, it has been practised to manually cleareach of such holes h by a punch r having an annular cutting edge e, orto mechanically clear the fins by using a lower die board 1 having aplurality of the punches r in conjunction with a cooperating upper dieboard u. The manual process is and expensive, while the lattermechanical process has a difficulty in that the locations of theclearing punches r on the lower die board are hard to align with thedesired hole positions of the rubber sheet s. Especially, when the sizeof the holes h is small, the alignment of the punches r with the desiredholes h is difficult to establish. If the punches r are not accuratelyaligned with the desired holes h, the round cutting edges e of thepunches r tend to deform the shape of the individual holes h, and hence,the

"recesses c integrally formed with the shaping surface of a pressureboard d coacting with a shaping press having a surface plate with aplurality of die projections f. The die recesses c are aligned with thedie projections f,

2 respectively. The cooperation of the die projections f and the dierecesses 0 results in the formation of a plurality. of fins p" which areoffset from the surface of the sheet s. The fins p" thus offset from thesurface of the sheet s can comparatively easily be cleared by simplebuffing or the like. The pressure board d with such die recesses c inaccurate alignment with the die projections f is difficult to make, andhence, it is very expensive. In addition, for achieving satisfactoryresults, careful and tedious maintenance work is necessary on thepressure board d.

Therefore, an object of the present invention is to obviate theaforesaiddifficulties of known processes of making multi-bored rubbersheets, by providing an improved method for making fin-free multi-boredrubber sheets. With the method according to the present invention, arubber sheet having a plurality of fin-free holes bored therethroughwith accurate dimensions of the size and position can be obtained,without necessitating any complicated finishing work or elaborate dies.

To fulfill the aforesaid object, the present invention uses a carriersheet to be overlaid on a starting rawrubber sheet. The startingraw-rubber sheet is laid on a die mounted on the surface plate of ashaping press, while directing the carrier sheet overlaid thereon towarda cooperating pressure board. When the pressure board is forced towardthe surface plate of the shaping press, die projections formed on thedie at the surface plate act to form desired holes on the startingraw-rubber sheet and to press resultant fins toward the carrier sheet.Upon completion of the shaping operation, the pressure board isseparated from the shaping press and the carrier sheet is removed fromthe multibored rubber sheet thus formed. The carrier sheet is such'thatthe fins which are pressed to the carrier sheet during the shapingoperation are separated from the multi-bored rubber sheet, as thecarrier sheet is removed from the multi-bored rubber sheet.

The carrier sheet to be used in the method of the present invention isrequired to ensure the smooth flow of raw-rubber material during theshaping operation, to withstand the pressure applied thereto during theshaping operation, and to be joined to those portions of the startingraw-rubber sheet which are pressed thereto by the die projections at apressure higher than a predetermined level. Such carrier sheet to beselectively joined to the starting raw-rubber sheet is, for instance, awoven cloth, a sheet of toughened paper, a rubber sheet, a plasticssheet, or a metallic sheet, all of which is specially treated so as tomeet the aforesaid conditions required for the carrier sheet. Theaforesaid selective joining of the carrier sheet to the startingraw-rubber sheet may be effected by twining the rawrubber material tothe texture of the woven cloth, or by any other mechanism suitable formeeting the aforesaid conditions.

The separation of the carrier sheet from the shaped multi-bored rubbersheet should preferably be carried ut while the latter is still warmbefore the multi-bored sheet is completely cooled, so that the finsformed during the shaping operation can easily be separated from therubber sheet without causing any significant scars thereon. When therubber sheet is still warm, the

rubber sheet is comparatively soft and the fins are easily separablefrom the sheet.

which:

FIGS. 1 and 2 are schematic diagrams, illustrating the conditionsof ashaping press before and after the shaping operation, according to themethod of the present invention;

FIG. 3 is a partial enlarged sectional view of the shaping pressillustrated in FIG. 2;

FIG. 4 is a diagrammatic illustration of the manner in which the finsare removed;

FIG. 5 is a schematic perspective view of a carrier sheet carrying aplurality of fins joined thereto;

FIG. 6 is a partial perspective view of a fin-free multibored rubbersheet, which is obtainable by the method according to the presentinvention;

FIG. 7 is a partial perspective view of a rubber sheet as formed by aconventional device for making multibored rubber sheet;

FIGS. 8 and 9-are schematic perspective views, illustrating a punch forremoving fins and a,press using a plurality of such punches,respectively;

' FIG. 10 is a schematic partial perspective view of a defectivemulti-bored rubber sheet caused by using an improper fin-removing punch;and

FIGS." 11 and 12 .are diagrammatic illustrations of another knownprocess for making multi-bored rubber sheets.

Like parts are designated by like numerals and symbols throughout thedrawings.

Referring to FIGS. 7 to 9, a multi-bored rubber sheet s made by a knownprocess includes fins pformed at one end of each hole h thereof. Inorder to remove such fins p, one or more punches r, each having anannular edge e have heretofore been used. Manual removal by using onlyone such punch r is time-consuming, and not practical on industrialscale. A plurality of such punches r may be secured to a lower die boardI in alignment with the holes h of the sheet s as shown in FIG. 9.. Ifsuch punches are fitted in the holes h of the sheet s and the sheet s ispressed toward the punches r by an upper board u, the fins p ofdifferent-holes h may be removed simultaneously in one stroke. Tosuccessfully carry out such simultaneous removal of the fins p, thepunches r must be accurately aligned with the holes h in the sheets. Ifthe punches are not aligned, the holes h maybe deformed by being cut bysuch punches, and it becomes impossible to produce accuratelydimensioned multi-bored rubbersheets. Anyone experienced in the artknows that such accurate alignment of the punches r with the desiredholes h is rather difficult to.

recesses c for receiving die projections f, as shown in FIG. 11. Withsuch second die d, the fins p are offset from the surface of the desiredmulti-bored rubber sheet s, as shown in FIG. 12. The offsetting of thefins from the rubber sheetsurface facilitates the removal of thefins-,-for instance, by simple buffing. It is, however,

difficult and time-consuming to form the recesses c of the second die din accuratealignment with the die projections f. If the recesses c arenot exactly aligned with the die projections f, the desired resultcannot be achieved.

Therefore, the essential object of the present invention is to mitigatethe aforesaid difficulties of the known processes for making multi-boredrubber sheets, by providing an improved method for making fin-freemulti-bored rubber sheets.

FIG. 1 illustrates a shaping press and a pressure board which can beused in the method for making finfree multi-bored rubber sheets,according to the present invention. A surface plate 1 of shaping presscarries a die 2 placed thereon. The die 2 includes a plurality of dieprojections 3 for shaping desired holes in the rubber sheet. The dieprojections 3 in FIG. 1 correspond to die projections f of the aforesaidconventional devices. A pressure board 4 has a surface which move towardand away from a plane of the free ends of the die projections 3, inparallel with latter plane. The assembly of the shaping press inclusiveof the surface plate 1 and the pressure board 4 is of knownconstruction, and can be actuated by aconventional driving means. Thesurface plate 1 and the pressure board 4 can also be used for thepurpose of vulcanization, in a manner well known to those skilled in theart.

A starting raw-rubber sheet w is placed on the die projections 3 of thedie 2. A carrier sheet t, such as a woven cloth, is spread on the uppersurface of the starting raw-rubber sheet w. Then, the pressure board 4is lowered by a suitable known means, such as a conventional hydraulicdrive, so that the starting raw-rubber sheet w and the carrier sheet tare pressed against the die 2, as shown in FIG. 2. Under suchconditions, the die projections 3 penetrate through the raw-rubber sheetw for shaping the desired holes h of the multibored rubber sheet.

Referring to FIG. 3, according to the present invention, the upper endof each die projection 3 strongly urges the corresponding part of theraw-rubber sheet w to the pressure board 4 through the carrier sheet tinserted therebetween. Although the starting'raw-ru bber sheet materialat the part facing the upper end of the die projection 3 mostly flows tothe periphery of the hole formed through the sheet w, it is inevitablethat a small portion of such raw-rubber material is left from theaforesaid flow so as toform a thin layer m, which is pressed into'thetexture of the carrier sheet 1. Consequently the thin layer m is joinedto the carrier sheet t.

If it is desired to have a very strong joint between the carrier sheet tand the aforesaid thin layer m, an additional thin rubber sheet or athin rubber lining may be applied on that surface of the carrier sheet twhich contacts the pressure board 4, so that the aforesaid thin layer mmay be communicated and joined to such additional thin rubber sheetthrough the carrier sheet t.

The multi-bored rubber sheet thus formed should preferably be vulcanizedbefore removing the pressure board 4 from the surface plate 1 of theshaping press. Upon completion of the vulcanization, the pressure board4 is raised, e.g., by a hydraulic means, so as to allow the removal ofthe carrier sheet t from the die 2, as shown in FIG. 4. When the carriersheet t leaves the die 2, the aforesaid thin layers m are removedtogether with the carriersheet t, as shown in FIG. 5. Thereby,

the starting raw-rubber sheet w is shaped into a fin-free multi-boredrubber sheet s, as shown in FIG. 6.

More particularly, each hole h in the multi-bored rubber sheet s made bya method according to the present invention has a clean and smooth edge,as can be seen from FIG. 6. Besides, the locations of the holes h can beaccurately established by means of the die 2 having the die projections3 integrally formed therewith in a precise fashion. It is an importantfeature of the present'invention that the desired fin-free multiboredrubber sheet having clean holes, which are accurately disposed atpredetermined intervals, can be produced by one simple process ofpressing followed by vulcanization in the state as pressed.

When a woven cloth is used as the carrier sheet I, the texture of thewoven cloth may be transferred to the surface of the fin-freemulti-bored rubber sheet s. Such texture, however, is not harmful at allif the multi-bored rubber sheet s is used as a sifting screen. If suchtexture is not desirable, it can easily be removed from the surface ofthe multi-bored rubber sheets s by simple buffing. If the carrier sheett has a smooth surface facing the multi-bored rubber sheet s, thesurface of the multi-bored rubber sheet s is, of course, made smoothwithout any undesirable patterns thereon.

As described in the foregoing disclosure, the present invention providesan improved method for making finfree multi-bored rubber sheets havingclear smooth holes of accurate dimensions with respect to the insidediameter and mutual locations thereof, simply by inserting a carriersheet between a starting raw-rubber sheet and a pressure board forpressing the starting raw-rubber sheet to a shaping die. The methodaccording to the present invention does not cause any significantcomplication in the shaping operation and does not use any elaboratelyshaped dies.

Thus, the present invention contributes greatly to the industry.

What is claimed is:

l. A method for making fin-free multi-bored rubber sheets, comprisingsteps of disposing a die having a plurality of die projections on thesurface plate of a shaping press, spreading a starting raw-rubber sheeton a plane of the free ends of the die projections, overlaying a carriersheet on the starting raw-rubber sheet, pressing the starting raw-rubbersheet together with the carrier sheet toward the die by means of a flatpressure board, said carrier sheet being of such material andconstruction that when those parts of the raw-rubber sheet which facethe free ends of the die projections are pressed against the'carriersheet by a pressure in excess of a certain value said parts of theraw-rubber sheet are 10 joined to the carrier sheet, moving saidpressure board away from the die, removing the carrier sheet from theraw-rubber sheet together with the said portions facing the free ends ofthe die projections, and removing the rubber sheet from the'die.

2. A method for making fin-free multi-bored rubber sheets, comprisingsteps of disposing a die having a plurality of die projections on thesurface plate of a shaping press, spreading a starting raw-rubber sheeton a plane of the free ends of the die projections, overlaying a carriersheet on the starting raw-rubber sheet, overlaying another layer of thinrubber on said carrier sheet pressing the starting raw-rubber sheettogether with the carrier sheet toward the die by means 0 a flatpressure board, said carrier sheet being of such material andconstruction that when those parts of the rawrubber sheet which face thefree ends of the die projections are pressed against the carrier sheetby a pressure in excess of a certain value said parts of the raw-rubbersheet are joined to the carrier sheet as well as to said thin rubberlayer through the carrier sheet, moving said pressure board away fromthe die, removing the carrier sheet from the raw-rubber sheet togetherwith the portions facing the free ends of the die projections, andremoving the rubber sheet from the die.

3. A method according to claim 1 and further comprising a step ofvulcanizing the rubber sheet by heating said die and said pressure boardafter said pressing prior to moving said pressure board.

4. A method according to claim 1, wherein said carri er sheet is made ofmaterial selected from the group consisting of a woven cloth, a sheet oftoughened paper, a rubber sheet, a plastics sheet, and a metallic sheet.

1. A method for making fin-free multi-bored rubber sheets, comprisingsteps of disposing a die having a plurality of die projections on thesurface plate of a shaping press, spreading a starting raw-rubber sheeton a plane of the free ends of the die projections, overlaying a carriersheet on the starting rawrubber sheet, pressing the starting raw-rubbersheet together with the carrier sheet toward the die by means of a flatpressure board, said carrier sheet being of such material andconstruction that when those parts of the raw-rubber sheet which facethe free ends of the die projections are pressed against the carriersheet by a pressure in excess of a certain value said parts of therawrubber sheet are joined to the carrier sheet, moving said pressureboard away from the die, removing the carrier sheet from the raw-rubbersheet together with the said portions facing the free ends of the dieprojections, and removing the rubber sheet from the die.
 2. A method formaking fin-free multi-bored rubber sheets, comprising steps of disposinga die having a plurality of die projections on the surface plate of ashaping press, spreading a starting raw-rubber sheet on a plane of thefree ends of the die projections, overlaying a carrier sheet on thestarting raw-rubber sheet, overlaying another layer of thin rubber onsaid carrier sheet, pressing the starting raw-rubber sheet together withthe carrier sheet toward the die by means of a flat pressure board, saidcarrier sheet being of such material and construction that when thoseparts of the raw-rubber sheet which face the free ends of the dieprojections are pressed against the carrier sheet by a pressure inexcess of a certain value said parts of the raw-rubber sheet are joinedto the carrier sheet as well as to said thin rubber layer through thecarrier sheet, moving said pressure board away from the die, removingthe carrier sheet from the raw-rubber sheet together with the portionsfacing the free ends of the die projections, and removing the rubbersheet from the die.
 3. A method according to claim 1 and furthercomprising a step of vulcanizing the rubber sheet by heating said dieand said pressure board after said pressing prior to moving saidpressure board.
 4. A method according to claim 1, wherein said carriersheet is made of material selected from the group consisting of a wovencloth, a sheet of toughened paper, a rubber sheet, a plastics sheet, anda metallic sheet.